Using plant chemistry to improve interactions between plants, herbivores and their natural enemies: challenges and opportunities

• Plant secondary metabolites can both help and harm natural enemies of herbivores. • Engineering natural enemies promotes positive effects of plant chemistry. • Resistance and attraction to plant metabolites enhances biocontrol potential. • Field experiments are needed to assess the costs and benefits of this approach. Plant secondary (or specialized) metabolites determine multitrophic interaction dynamics. Herbivore natural enemies exploit plant volatiles for host location and are negatively affected by plant defense chemicals that are transferred through herbivores. Recent work shows that herbivore natural enemies can evolve resistance to plant defense chemicals, and that generating plant defense resistance through forward evolution enhances their capacity to prey on herbivores. Here, we discuss how this knowledge can be used to engineer better biocontrol agents. We argue that herbivore natural enemies which are adapted to plant chemistry will likely enhance the efficacy of future pest control efforts. Detailed phenotyping and field experiments will be necessary to quantify costs and benefits of optimizing chemical links between plants and higher trophic levels.